The function of HEXIM1 (HEXIM P-TEFb complex subunit 1, Ensembl gene identifier ENSG00000186834) is as follows. Transcriptional regulator which functions as a general RNA polymerase II transcription inhibitor (PubMed:14580347, PubMed:15201869, PubMed:15713661). Core component of the 7SK RNP complex: in cooperation with 7SK snRNA sequesters P-TEFb in a large inactive 7SK snRNP complex preventing RNA polymerase II phosphorylation and subsequent transcriptional elongation (PubMed:12832472, PubMed:14580347, PubMed:15201869, PubMed:15713661). May also regulate NF-kappa-B, ESR1, NR3C1 and CIITA-dependent transcriptional activity (PubMed:15940264, PubMed:15941832, PubMed:17088550). Plays a role in the regulation of DNA virus-mediated innate immune response by assembling into the HDP-RNP complex, a complex that serves as a platform for IRF3 phosphorylation and subsequent innate immune response activation through the cGAS-STING pathway (PubMed:28712728). {ECO:0000269|PubMed:12581153, ECO:0000269|PubMed:12832472, ECO:0000269|PubMed:14580347, ECO:0000269|PubMed:15201869, ECO:0000269|PubMed:15713661, ECO:0000269|PubMed:15940264, ECO:0000269|PubMed:15941832, ECO:0000269|PubMed:17088550, ECO:0000269|PubMed:28712728}.